By adopting a new voltage-withstanding structure consisting of a series of alternately arranged P-type and N-type semiconductor thin layers, a superjunction device has an advantage that both the P-type and N-type semiconductor thin layers can be fully depleted at a relative low voltage in an off-state, enabling the compensation of electric charges, and thereby exhibiting a high breakdown voltage even if the P-type and N-type semiconductor thin layers have a relatively high impurity concentration, thus achieving a low on resistance and a high breakdown voltage at the same time. U.S. Pat. No. 5,216,275 discloses the above-mentioned alternately arranged P-type and N-type semiconductor thin layers, wherein the thin layers are in contact with an N+ substrate. U.S. Pat. No. 6,630,698 also discloses the above-mentioned alternately P-type and N-type semiconductor thin layers, wherein the semiconductor thin layers in a central region may be separated from the N+ substrate by a distance greater than zero.
In the prior art, the P-type and N-type semiconductor thin layers can be formed by repeating a process of epitaxial growth followed by photolithography and implantation until a total thickness of the P-type and N-type semiconductor thin layers meets a desired value. For a MOSFET with a breakdown voltage higher than 600V, the process generally needs to be repeated for more than 5 times, resulting in a high manufacturing cost and a long production cycle. Another way to form P-type and N-type semiconductor thin layers is to grow an epitaxial layer of a certain type to a desired thickness in one time, and then etch trenches and fill the trenches with a silicon of the opposite type, so as to reduce the manufacturing cost and shorten the production cycle. However, if there is a distance between the semiconductor thin layers and the substrate, the depths of the trenches in different devices are likely to vary due to the variations in process conditions during trench-etching, which may lead to a great difference in reverse breakdown voltage among different devices. Especially, in the case that the distance between the N+ substrate and the bottom of the trenches is smaller than a certain value, not only the breakdown voltage of a device is likely to vary according to the process conditions, but also the capability of sustaining current surge, such as the single pulse avalanche energy (EAS), of a device is likely to vary according to the process conditions, which will greatly affect the uniformity of the devices.